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Lose of pressure

Have a 2008 Toyota Tacoma 4.0L, went to bleed brakes noticed I wasnt getting any pressure to the rear but plenty to the front. After further investigation and chasing fluid the master cylinder was only squirting to front and not rear. So thinking it was faulty purchased a new one bench bled it and had pressure from both holes, hooked it up and still the same thing…so after a 3rd master I still have the same problem. I have no idea what is going here so if anyone can help I’m open for suggestions.

Bad proportioning valve?

Any idea where that maybe

Does this truck have 4 wheel ABS ? If so, you can’t bleed them the normal way.

You need a special tool to activate the ABS unit, might be able to rent one, or take it to a brake shop or dealer to have brakes properly bled.

I’ve heard it can be done by going fast enough on a gravel road and slamming on the brakes to activate the ABS, then bleed and repeat as needed.

First try unplugging the ABS unit. On some vehicles this is required in order to bleed the brakes properly, but that won’t bleed the ABS module itself. For that, you need a scan tool that runs an ABS bleed program.

If you’ve got the time and don’t want to spend money on tools and/or a trip to a shop . . .

You can always try gravity bleeding

Usually in the brake line going to the rear but near the firewall.

On my 2004 Chrysler Town and Country the owners manual warned against trying to bleed the brakes and said it could only be done at the dealer.

My 2012 Camry has 4 wheel ABS and I had no trouble bleeding the brakes at all.

I concur w/the above advice, thinking the problem is ABS related. The problem with this theory however is it doesn’t explain why – presumably after disconnecting both MC hoses – the original MC wasn’t squirting from the rear port. That part remains a mystery. I suppose it is possible that there is an actual problem with the rear wheel hydraulic flow, and for some reason that damaged the original MC’s rear seals.

If I had that problem and was certain it wasn’t the ABS bleeding procedure I was using I’d connect up a hand-held pump, loosen both rear wheel brake bleeders, and try to pump fluid through the rear lines to see if it flowed or not.

Just an update what’s going on, I’ve checked for a proportioning valve and considering that it has a lift it was removed cause it’s no where to be found. I do believe its ABS related due to some temporary switching of lines (rear with front) from the top of ABS which in return allowed pressure to the whole right side of vehicle and not the left.

Maybe a couple of brake lines got installed in the the wrong ABS port during the custom lift job. If there’s no proportioning valve and there should be, for safety considerations suggest to get that issue resolved as part of fixing this problem. As far as inadvertently swapping lines, I’ve done it. Not w/brake lines, but few years ago I was working on my truck’s fuel system and got the two return lines to the two tanks swapped. I noticed when I drove the truck the fuel gauge on tank 1 would rapidly go down, while the gauge on tank 2 would rapidly go up … lol .